Swaging machine

ABSTRACT

Means are provided which define a path of travel for a workpiece to be swaged through a machine housing. Four hydraulic cylinderpiston motors extend in said housing radially with respect to said path and are angularly spaced 90* apart around said path. Shaping tools are operatively connected to said cylinder-piston motors and operable to penetrate into a workpiece traveling along said path. Each of said cylinder-piston motors comprises a cylinder and a piston having a larger piston face remote from said path and a smaller piston face adjacent to said path. Each of said cylinders has an outer chamber defined by said larger piston face and an inner chamber defined by said smaller piston face. Said cylinder-piston motors are arranged to form two pairs of adjacent motors. Two pump units are provided, each of which is laterally secured to said housing and associated with one of said pairs of motors. Each of said pump units comprises two larger piston pumps having pistons relatively large in diameter and two smaller piston pumps having pistons relatively small in diameter. Each of said larger pumps is connected to said outer chamber of one of said cylinders of the associated pair of motors. Each of said smaller pumps is connected to said inner chamber of one of said cylinders of the associated pair of motors. Drive means are provided to synchronously drive said pistons of said larger pumps of both said pump units and said pistons of said smaller pumps of both said pump units to apply mutually assisting forces to said larger and smaller piston faces of each of said cylinder-piston motors.

n51 3,6d5,l2o

[ 51 Feb. 29, 1972 llnited States Patent Kralowetz et al.

[54] SWAGHNG MACHINE [57] ABSTRACT Means are provided which define a path of travel for a work- [72] Inventors: Bruno Kralowetz, St. Ulrich Bei Steyr;

Johann Braunwieser, Steyr, both of Austria piece to be swaged through a machine housing. Four hydraulic cylinder-piston motors extend in said housing radially with [73] Asslgnee GFM Gesellsfhah fur Fmzfigungstechmk respect to said path and are angularly spaced 90 apart around and Mascmnenba Aknengeseuschafl said path. Shaping tools are operatively connected to said steyr' Ausma cylinder-piston motors and operable to penetrate into a work- June 22, 1970 [21] Appl. No.: 48,126

[22] Filed; piece traveling along said path. Each of said cylinder-piston motors comprises a cylinder and a piston having a larger piston face remote from said path and a smaller piston face adjacent to said path. Each of said cylinders has an outer chamber defined by said larger piston face and an inner [30] Foreign Apphcamm Pnomy Data chamber defined by said smaller piston face. Said cylinder- June 27, 1969 Austria ....A 6135/69 piston motors are arranged to form two pairs of adjacent motors. Two pump units are provided, each of which is laterally secured to said housing and associated with one of said pairs [52] US. Cl. 72/453, 60/545 H .B2ld 41/00, B2lj 9/18 .72/402, 453; 60/545 H, 54.6 H

[51] Int.Cl. of motors. Each of said pump units comprises two larger piston pumps having pistons relatively large in diameter and two smaller piston pumps having pistons relatively small in [58] Field of Search diameter. Each of said larger pumps is connected to said outer References Cited chamber of one of said cylinders of the associated pair of mo- UNlTED STATES PATENTS tors. Each of said smaller pumps is connected to said inner chamber of one of said cylinders of the associated pair of mo- 443,029 12/1890 443,030 12/1890 Wood.....

tors. Drive means are provided to synchronously drive said pistons of said larger pumps of both said pump units and said pistons of said smaller pumps of both said pump units to apply mutually assisting forces to said larger and smaller piston faces of each of said cylinder-piston motors.

Primary ExaminerCharles Wv Lanham Assistant Examiner-Michael .l. Keenan Attorney-Kurt Kelman l2 Clalms, 3 Drawlng Flgures SWAGING MACHINE This invention relates to a swaging machine which comprises four hydraulic cylinder-piston motors, which serve to move the shaping tools and extend radially to the axis of the workpiece and are angularly spaced 90 apart.

Such swaging machines are mainly intended to shape workpieces which have large cross-sectional dimensions and which consist of such a material that difficulties may arise when an ingot of the material is directly rolled. The shaping of such workpieces involves large moments so that the mechanically driven, known swaging machines which are satisfactory for other purposes would require driving members which are so large that the manufacture of the machine would be uneconomical.

A swaging machine which comprises hydraulically driven shaping tools is already known. In that machine, the pistons of the four cylinder-piston motors are caused to perform working strokes by four pump pistons, which are rigidly mounted in juxtaposed relation on another reciprocating piston or the like and disposed in pump cylinders which communicate with those cylinder chambers of the cylinder-piston motors which are remote from the workpiece. Separate retracting pistons are provided to retract the shaping tools from the workpiece. Hydraulic accumulators are provided to apply pressure to respective retracting pistons. The desired cross-sectional dimensions of the workpiece determine the depth to which the shaping tools should penetrate the workpiece. For this reason, workpieces having different dimensions can be produced only if the dead center positions of the pistons are variable. For this purpose, each cylinder-piston motor in the known machine is provided with a mechanically adjustable stop, which determines the dead center position of the piston remote from the workpiece. Because the stroke of the pistons is always the same, as it depends on the stroke of the pump pistons, the change of the initial position of the working pistons by means of the adjustable stop will result also in a change of the second dead center position of the piston and of the depth to which the tools penetrate the workpiece. The retracting pistons serve to retract the working pistons to the stops. That known machine has various disadvantages. Because the pump pistons for all four cylinder-piston motors are combined in one station, some of the conduits which connect the pump cylinders to the cylinders of the cylinder-piston motors are relatively long. Because the hydraulic fluid is compressible to some extent and the conduits are elastically deformable, the high pressures which arise may result in vibration and the like phenomena in the hydraulic systems so that an exact swaging to predetermined dimensions may not be possible. Besides, a compact arrangement of closely spaced parts cannot be provided in the known machine. The retracting pistons and the hydraulic accumulators considerably add to the structural expenditure, which is further increased by the mechanical means which are required to adjust the stops for the pistons of the cylinder-piston motor. Finally, it is difficult to make up for leakage losses.

It is an object of the invention to eliminate these disadvantages and to provide a swaging machine which is of the kind defined first hereinbefore and which is relatively simple in design, and has a compact arrangement and in which vibration or the like phenomena in the hydraulic systems are minimized, there is no need for mechanically adjustable stops to control the dead center positions of the pistons of the cylinder-piston motors, the dimensions to which the workpiece is swaged are continuously checked, and leakage losses are continuously compensated.

This object is accomplished according to the invention essentially in that the pistons of the cylinder-piston motors are double acting, two pump units are provided, which are laterally secured to the machine housing and each of which is associated with two cylinder-piston motors which are adjacent to each other, each of said pump units comprises two larger piston pumps having pistons which are relatively large in diameter, two smaller piston pumps, and an eccentric shaft which carries two eccentric members, each of which drives by means of an elliptic chuck or the like a larger piston pump and a smaller piston pump which is disposed opposite to and coaxial with said larger piston pump, the larger piston pumps are connected to those cylinder chambers of the cylinder-piston motors which are remote from the workpiece and defined by a relatively large piston face, the smaller piston pumps are connected to the other cylinder chambers of the cylinder-piston motors, and the motors for driving the eccentric shafts of both pump units are synchronized. Because each pump unit is associated with two cylinder-piston motors which are adjacent to each other, the pump unit may be secured to the machine housing very close to the cylinder-piston motors so that the length of the conduits which connect the pump cylinders to the cylinder chambers of the cylinder-piston motors is minimized, the liquid cushions are relatively small and vibration or the like phenomena in the hydraulic systems are avoided to a large extent. Besides, the overall arrangement is simple, compact and clear. Communicating with those cylinder chambers of the cylinder-piston motors which are remote from the workpiece and defined by a relatively large piston face, the two larger piston pumps impart the working stroke to the pistons of these motors. Communicating with those-cylinder chambers of the cylinder-piston motors which are adjacent to the workpiece and defined by the smaller piston faces, the smaller piston pumps serve to retract the pistons so that accumulators are not required for this purpose. Because the piston pumps are arranged in pairs, each of said pairs comprise a larger piston pump and a smaller piston pump which is disposed opposite to and coaxial with the larger piston pumps, and the pumps of each pair are driven by the same eccentric member, the pistons of these pumps move in mutually opposite directions so that a pressure stroke of one pump piston is necessarily accompanied by a suction stroke of the other pump piston and mutually assisting forces can be applied in a simple manner to the two ends of each piston of the cylinder-piston motors, as is required. The arrangement may be such that one of the two piston pumps which are driven by a common eccentric is associated with one cylinder-piston motor and the other of said pumps is associated with the other cylinder-piston motor so that the length of the connecting conduits is further reduced. A synchronous operation of all four cylinder-piston motors is ensured in that each eccentric shaft drives two of said motors and the motors for driving the two eccentric shafts are mechanically or electrically synchronized. It will be understood that the eccentric shafts may be replaced by crankshafts and the elliptic chucks may be replaced by corresponding connecting rods or the like.

A relief valve is preferably associated with that cylinder chamber of each cylinder-piston motor which is remote from the workpiece and defined by the larger piston face. This relief valve will open when a predetermined swaging force is exceeded so that a reliable overload protection is provided with simple means.

In a development of the invention, the amounts of the hydraulic fluid contained in the hydraulic systems comprising the larger piston pumps and those cylinder chambers of the cylinder-piston motor which are defined by the larger piston face, on the one hand, and the smaller piston pumps and those cylinder chambers of the cylinder-piston motors which are adjacent to the workpiece, on the other hand, are variable in mutually opposite senses. In this manner the dead center positions of the pistons of the cylinder-piston motors and the depth of penetration of the shaping tools into the workpiece can be varied without need for a mechanically adjustable stop or the like for this purpose because a reduction of the amount of liquid at one end of a piston of a cylinder-piston motor and a simultaneous increase of the amount of liquid at the other end of the piston will obviously result in a corresponding movement of the piston. This hydraulic control of the dead center positions has mainly the advantage that the dead center positions of the piston may be changed also during operation so that corrections are enabled during the operation of the machine.

101025 nn'm To enable a change of the amount of hydraulic fluid in the hydraulic systems, each hydraulic system is provided, in accordance with the invention, with a separate filling pump, the filling pump for the systems which comprise the larger piston pumps and those cylinder chambers of the cylinder-piston motors which are defined by the larger piston faces consist of reversible pumps, and each of the other systems is provided with a relief valve. The reversible pumps can remove hydraulic fluid from the respective hydraulic systems so that there is no need to apply a particularly high pressure during an adjustment of the piston away from the workpiece whereas such high pressure would otherwise be required owing to the smaller piston face. On the other hand, an adjustment of the piston toward the workpiece can be effected by a pressure which will not cause the relief valve to open because a much larger piston face is available for this adjustment.

According to another proposal of the invention, each conduit from a reversible pump to the hydraulic system which includes the larger piston pump is provided with a receiver and/or a relief valve and/or the like and has an outlet formed by a valve port which is arranged to be closed by the piston of the larger piston pump during the movement thereof so that said conduit is open only when the piston of the cylinderpiston motor does not apply shaping pressure or applies only a low shaping pressure to the workpiece. This arrangement results in a port control which ensures that the high shaping pressure will not act on the reversible pump and that the latter need not discharge against the high shaping pressure. When the pump piston closes the valve port, the liquid delivered by the reversible pump is drained through the relief valve or is stored.

To enable a high-speed adjustment when the machine is in operation but does not swage, each valve port or the like is bypassed by a gate valve or the like, which can directly connect the conduit from the reversible pump to the conduit leading from the larger piston pump to the corresponding cylinder chamber ofthe cylinder-piston motor.

In a further development of the invention, each cylinderpiston motor is provided with an electric position sensor, which senses that dead center position of the piston which corresponds to the deepest penetration of the shaping tool into the workpiece and a controller is provided, which compares the signals delivered by the sensors with signals representing predetermined, desired values and in response to a difference produces control signals for automatically reversing the reversible pump. If the actual dead center position of the piston differs from the predetermined, desired position, e.g., as a result of leakage losses, the reversible pump will be reversed until the desired position has been assumed so that the dimensions of the swaged workpiece will be continuously checked. Leakage losses are continuously compensated by the reversible pump and are even desirable because the temperature of the liquid rises during operation and an addition of cool liquid will avoid an excessive temperature rise.

An embodiment ofthe invention is shown by way of example on the accompanying drawings, in which FIG. 1 is a simplified sectional view showing a swaging machine and taken transversely to the axis of the workpiece.

FIG. 2 is a sectional view taken on line lI-II of FIG. 1 and taken through a pump unit, and

FIG. 3 is a diagram representing the hydraulic system of one half of the machine.

A machine housing or swaging machine box 1 contains four hydraulic cylinder-piston motors 3, 4, 5, 6, which extend radially to the axis of a workpiece 2 and are angularly spaced 90 apart and inclined 45 from the horizontal. Each of said motors comprises a piston 7. Shaping tools 8 are directly secured to the forward end faces of said pistons 7. Each piston 7 is double acting. The cylinder-piston motors are arranged in two pairs 3, 4 and 5, 6. Two pump units 9, 10 are laterally secured to the machine housing 1. Each pump unit is associated with one pair of cylinder-piston pumps 11, 11 or 12, 12 having pistons which are relatively large in diameter, and two smaller pumps l3, 13' or l4, 14'. The larger piston pumps 11, 11 and l2, 12 are connected to those cylinder chambers 15 of the cylinder-piston motors 3-6 which are remote from the workpiece. Those cylinder chambers 16 of the cylinder-piston motors which are adjacent to the workpiece 2 and defined by a much smaller piston face are connected to the smaller piston pumps 13, 13' and 14, 14. Hence, the larger piston pumps impart a working stroke to the pistons 7 of the hydraulic cylinder-piston motors 3-6 whereas the smaller piston pumps retract the pistons 7 to their initial position.

Each pump unit 9, 10 comprises an eccentric shaft 17, which carries two eccentric members 18. Motors 19 for driving the eccentric shafts 17 are synchronized. Each eccentric member 18 is embraced by a link 19, which is slidable on a spider 20 of an elliptic chuck. The spider 20 directly carries the pistons of the piston pumps so that these pumps form guides for the spider. Each of the larger piston pumps 11, 11', 12, 12 is disposed opposite to and coaxial with one of the smaller piston pumps 13', 13, 14, 14. These two opposite and coaxial pumps are driven by the same eccentric member 18 so that the conduits from each side of the pump unit lead to the same cylinder-piston motor and the two cylinder chambers 15, 16 of each of the cylinder-piston motors 3-6 are automatically subjected to mutually assisting forces.

In accordance with FIG. 3, a relief valve 21 is associated with each cylinder chamber 15 and is arranged to open when a predetermined pressure or swaging force is exceeded during the working stroke of the pistons 7 so that the relief valve prevents an overloading of the machine. To change the dead center positions ofthe pistons 7, the depth to which the tools 8 penetrate into the workpiece and the cross-sectional dimensions of the workpiece, the amount of hydraulic fluid can he changed which is contained in the hydraulic systems comprising the piston pumps ll, 11' and cylinder chambers 15, on the one hand, and the piston pumps l3, l3 and the cylinder chambers 16, on the other hand. For this purpose, a filling pump 22 and a relief valve 23 are provided for each system which comprises the smaller piston pumps 13 or 13' and the cylinder chambers 16 and a reversible pump 24 is provided for each system comprising a larger piston pump 11 or 11' and a cylinder chamber 15. To reduce the diameter of the workpiece, the reversible pumps 24 are operated to supply liquid into the cylinder chambers 15 whereas a corresponding amount of liquid is drained from the cylinder chambers 16 through relief valves 23. To increase the cross-sectional dimensions of the workpiece, the pumps 22 pump liquid into the cylinder chambers 16 and the reversible pumps 24 are set to suck liquid from the cylinder chambers 15.

Because a filling of the cylinder chambers 15 during the actual swaging work would require a very high pump pressure, conduits 27 extending from the reversible pumps 24 and provided with a receiver 25 and a relief valve 26 terminate in a valve port 28 in the larger piston pumps 11, 11'. This valve port is closed by the piston of the pump when the pistons 7 of the cylinder-piston motors 3-6 exert a relatively high shaping pressure on the workpiece. Hence, the discharge conduits 27 of the reversible pumps 24 are open only when there is no need to overcome an excessively high pressure in the respective hydraulic systems. The receivers 25 and the relief valves 26 will receive fluid as long as the pump pistons close the valve ports 28. Each conduit 27 is provided with a gate valve 29 or the like, which is adapted to connect the conduit 27 directly to a conduit 30 leading from the respective larger piston pump 11, 11' to the cylinder chambers 15. The filling pumps 24 are driven by a common motor 31.

Each cylinder-piston motor 3-6 is provided with an electric position sensor, which cooperates with a scale or the like to measure that dead center position of the piston which corresponds to the largest depth of penetration of the shaping tool 8 into the workpiece. Signals representing the measured values are fed by lines 33 to a controller 34 and are compared in the latter with signals which represent predetermined desired positions. In response to any difference, the controller delivers output signals through lines 35 to control means 36 for an automatic reversal of the reversible pumps 24.

We claim:

1. A swaging machine, which comprises a machine housing,

means defining a path of travel for a workpiece to be swaged through said housing,

four hydraulic cylinder-piston motors which extend in said housing radially with respect to said path and are angularly spaced 90 apart around said path,

shaping tools operatively connected to said cylinder-piston motors and operable to penetrate into a workpiece traveling along said path,

each of said cylinder-piston motors comprising a cylinder and a piston having a larger piston face remote from said path and a smaller piston face adjacent to said path,

each of said cylinders having an outer chamber defined by said larger piston face and an inner chamber defined by said smaller piston face,

said cylinder-piston motors being arranged to form two pairs of adjacent motors,

said machine also comprising two pump units, each of which is laterally secured to said housing and associated with one of said pairs of motors,

each of said pump units comprising two larger piston pumps having pistons relatively large in diameter and two smaller piston pumps having pistons relatively small in diameter,

each of said larger pumps being connected to said outer chamber of one of said cylinders of the associated pair of motors,

each of said smaller pumps being connected to said inner chamber of one of said cylinders of the associated pair of motors,

said machine also comprising drive means for synchronously driving said pistons of said larger pumps of both said pump units and said pistons of said smaller pumps of both said pump units to apply mutually assisting forces to said larger and smaller piston faces of each of said cylinder-piston motors.

2. A machine as set forth in claim 1, in which each of said larger pumps is disposed opposite to and coaxial with one of said smaller pumps of the same pump unit, and

said drive means comprise in each of said pump units an eccentric shaft carrying two eccentric members, and two elliptic chucks, each of which operatively connects one of said eccentric mem bers to one of said larger pumps and to the smaller pump which is opposite thereto and coaxial therewith in the same pump unit and two synchronously operable drive motors, each of which is operable in synchronism with the other to drive one of said eccentrics.

' 3. A machine as set forth in claim 1, which comprises four relief valves, each of which communicates with the outer chamber of one of said cylinders.

4. A swaging machine as set forth in claim 1, which comprises first hydraulic systems, each of which comprises at least one of said outer chambers and the larger pump connected thereto,

second hydraulic systems, each of which comprises at least one of said inner chambers and the smaller pump connected thereto, and control means for changing the amounts of hydraulic liquid 5 in said first systems and in said second systems in mutually opposite senses. 5. A swaging machine as set forth in claim 4, in which said control means comprise reversible pump means connected to said first systems, filling pump means connected to said second systems, and relief valve means connected to said second systems. 6. A swaging machine as set forth in claim 5, in which each of said first hydraulic systems comprises two of said outer chambers of one of said pairs of motors and said larger pumps connected thereto, each of said second hydraulic systems comprises one of said inner chambers and said smaller pump connected thereto, said reversible pump means comprise two reversible pumps,

each of which is connected to one of said first systems, said filling pump means comprise four filling pumps, each of which is connected to one of said second systems, and said relief valve means comprise four relief valves, each of which is connected to one of said second systems. 7. A swaging machine as set forth in claim 5, in which each of said larger piston pumps comprises a cylinder formed with a valve port arranged to be closed by the piston of said pump when said piston of said pump is in any position in which a substantial pressure is applied by said shaping tools to a workpiece traveling along said path, four conduits are provided, which connect said ports to said reversible pump means, and fluid-receiving means are connected to each of said conduits and arranged to receive hydraulic fluid delivered by said reversible pump means to said conduit when said port is closed by said piston. 8. A swaging machine as set forth in claim 7, in which said fluid-receiving means comprise a receiver.

9. A swaging machine as set forth in claim 7, in which said fluid-receiving means comprise a relief valve.

10. A swaging machine as set forth in claim 7, in which said fluid-receiving means comprise a receiver and a relief valve. 11. A swaging machine as set forth in claim 7, in which each of said larger pumps is connected to one of said outer chambers by a transfer conduit, each of said transfer conduits is connected by a bypass conduit to said reversible pump means, and an arbitrarily operable shutoff valve is included in each of said bypass conduits. 12. A swaging machine as set forth in claim 5, which comprises four electric position sensors operable to produce output signals representing an inner dead center position of the 5 5 pistons of respective cylinder-piston motors, and

control means operable to compare said signals with predetermined reference signals and to control said reversible pump means in response to the difference between said output signals and reference signals. =l =1:

mm: mun 

1. A swaging machine, which comprises a machine housing, means defining a path of travel for a workpiece to be swaged through said housing, four hydraulic cylinder-piston motors which extend in said housing radially with respect to said path and are angularly spaced 90* apart around said path, shaping tools operatively connected to said cylinder-piston motors and operable to penetrate intO a workpiece traveling along said path, each of said cylinder-piston motors comprising a cylinder and a piston having a larger piston face remote from said path and a smaller piston face adjacent to said path, each of said cylinders having an outer chamber defined by said larger piston face and an inner chamber defined by said smaller piston face, said cylinder-piston motors being arranged to form two pairs of adjacent motors, said machine also comprising two pump units, each of which is laterally secured to said housing and associated with one of said pairs of motors, each of said pump units comprising two larger piston pumps having pistons relatively large in diameter and two smaller piston pumps having pistons relatively small in diameter, each of said larger pumps being connected to said outer chamber of one of said cylinders of the associated pair of motors, each of said smaller pumps being connected to said inner chamber of one of said cylinders of the associated pair of motors, said machine also comprising drive means for synchronously driving said pistons of said larger pumps of both said pump units and said pistons of said smaller pumps of both said pump units to apply mutually assisting forces to said larger and smaller piston faces of each of said cylinder-piston motors.
 2. A machine as set forth in claim 1, in which each of said larger pumps is disposed opposite to and coaxial with one of said smaller pumps of the same pump unit, and said drive means comprise in each of said pump units an eccentric shaft carrying two eccentric members, and two elliptic chucks, each of which operatively connects one of said eccentric members to one of said larger pumps and to the smaller pump which is opposite thereto and coaxial therewith in the same pump unit and two synchronously operable drive motors, each of which is operable in synchronism with the other to drive one of said eccentrics.
 3. A machine as set forth in claim 1, which comprises four relief valves, each of which communicates with the outer chamber of one of said cylinders.
 4. A swaging machine as set forth in claim 1, which comprises first hydraulic systems, each of which comprises at least one of said outer chambers and the larger pump connected thereto, second hydraulic systems, each of which comprises at least one of said inner chambers and the smaller pump connected thereto, and control means for changing the amounts of hydraulic liquid in said first systems and in said second systems in mutually opposite senses.
 5. A swaging machine as set forth in claim 4, in which said control means comprise reversible pump means connected to said first systems, filling pump means connected to said second systems, and relief valve means connected to said second systems.
 6. A swaging machine as set forth in claim 5, in which each of said first hydraulic systems comprises two of said outer chambers of one of said pairs of motors and said larger pumps connected thereto, each of said second hydraulic systems comprises one of said inner chambers and said smaller pump connected thereto, said reversible pump means comprise two reversible pumps, each of which is connected to one of said first systems, said filling pump means comprise four filling pumps, each of which is connected to one of said second systems, and said relief valve means comprise four relief valves, each of which is connected to one of said second systems.
 7. A swaging machine as set forth in claim 5, in which each of said larger piston pumps comprises a cylinder formed with a valve port arranged to be closed by the piston of said pump when said piston of said pump is in any position in which a substantial pressure is applied by said shaping tools to a workpiece traveling along said path, four conduits are provided, which connect said ports to said reversible pump means, and fluid-receiving means are connected to each Of said conduits and arranged to receive hydraulic fluid delivered by said reversible pump means to said conduit when said port is closed by said piston.
 8. A swaging machine as set forth in claim 7, in which said fluid-receiving means comprise a receiver.
 9. A swaging machine as set forth in claim 7, in which said fluid-receiving means comprise a relief valve.
 10. A swaging machine as set forth in claim 7, in which said fluid-receiving means comprise a receiver and a relief valve.
 11. A swaging machine as set forth in claim 7, in which each of said larger pumps is connected to one of said outer chambers by a transfer conduit, each of said transfer conduits is connected by a bypass conduit to said reversible pump means, and an arbitrarily operable shutoff valve is included in each of said bypass conduits.
 12. A swaging machine as set forth in claim 5, which comprises four electric position sensors operable to produce output signals representing an inner dead center position of the pistons of respective cylinder-piston motors, and control means operable to compare said signals with predetermined reference signals and to control said reversible pump means in response to the difference between said output signals and reference signals. 